TOWARDS THE ULTIMATE LIMITS OF DEPTH RESOLUTION IN SPUTTER PROFILING - BEAM-INDUCED CHEMICAL-CHANGES AND THE IMPORTANCE OF SAMPLE QUALITY

Recent progress in materials characterization by sputter profiling is discussed, with particular emphasis on a critical evaluation of the parameters that determine the depth resolution. The net effect of beam-induced material transport and sputtering can be studied in a straightforward manner using abrupt doping distributions embedded in the matrix of interest, parallel to its flat surface. It is shown that the quality of the data that can be obtained with modern instruments is sufficient to identify lack of sample quality in terms of either surface flatness or abruptness of the doping distributions. Except for the presence of special artefacts, the depth resolution is always improved by using as low a bombardment energy as possible. The optimum angle of beam incidence depends on the crystalline structure of the sample as well as on the chemical identity of the primary ions. With oxygen primary ions a rather complex situation is encountered. Compared to inert gas ions, an improvement or a degradation in depth resolution may be achieved, depending on the impurity-matrix system under study. The merits of sample rotation are also discussed.